CN114804028A - Crack-free yttrium hydride neutron moderating material for space reactor and preparation method thereof - Google Patents
Crack-free yttrium hydride neutron moderating material for space reactor and preparation method thereof Download PDFInfo
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- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 title claims abstract description 139
- 229910000047 yttrium hydride Inorganic materials 0.000 title claims abstract description 95
- 239000000463 material Substances 0.000 title claims abstract description 81
- 238000002360 preparation method Methods 0.000 title abstract description 12
- 229910052739 hydrogen Inorganic materials 0.000 claims abstract description 61
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims abstract description 54
- 239000001257 hydrogen Substances 0.000 claims abstract description 54
- 229910052751 metal Inorganic materials 0.000 claims abstract description 45
- 239000002184 metal Substances 0.000 claims abstract description 45
- 238000000034 method Methods 0.000 claims abstract description 41
- 229910052727 yttrium Inorganic materials 0.000 claims abstract description 36
- 238000005245 sintering Methods 0.000 claims abstract description 27
- 238000005984 hydrogenation reaction Methods 0.000 claims abstract description 24
- 239000012535 impurity Substances 0.000 claims abstract description 20
- 238000003825 pressing Methods 0.000 claims abstract description 15
- 238000000465 moulding Methods 0.000 claims abstract description 14
- 230000008569 process Effects 0.000 claims description 26
- 238000001816 cooling Methods 0.000 claims description 8
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 claims description 7
- 229910052750 molybdenum Inorganic materials 0.000 claims description 7
- 239000011733 molybdenum Substances 0.000 claims description 7
- 238000007373 indentation Methods 0.000 claims description 5
- 229910052742 iron Inorganic materials 0.000 claims description 5
- 239000002245 particle Substances 0.000 claims 1
- 125000004435 hydrogen atom Chemical group [H]* 0.000 abstract description 7
- 238000004663 powder metallurgy Methods 0.000 abstract description 6
- 239000000203 mixture Substances 0.000 abstract description 5
- 238000004519 manufacturing process Methods 0.000 abstract description 4
- 239000013078 crystal Substances 0.000 abstract description 3
- 230000000694 effects Effects 0.000 abstract description 3
- 238000010521 absorption reaction Methods 0.000 description 7
- 230000008859 change Effects 0.000 description 6
- 239000012071 phase Substances 0.000 description 6
- 238000006243 chemical reaction Methods 0.000 description 5
- 238000005336 cracking Methods 0.000 description 5
- 230000004992 fission Effects 0.000 description 4
- 150000004678 hydrides Chemical class 0.000 description 4
- 230000007547 defect Effects 0.000 description 3
- 238000001514 detection method Methods 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- 229910052987 metal hydride Inorganic materials 0.000 description 3
- 150000004681 metal hydrides Chemical class 0.000 description 3
- 239000000843 powder Substances 0.000 description 3
- 230000009467 reduction Effects 0.000 description 3
- 229910052721 tungsten Inorganic materials 0.000 description 3
- QSGNKXDSTRDWKA-UHFFFAOYSA-N zirconium dihydride Chemical compound [ZrH2] QSGNKXDSTRDWKA-UHFFFAOYSA-N 0.000 description 3
- 229910000568 zirconium hydride Inorganic materials 0.000 description 3
- XLYOFNOQVPJJNP-ZSJDYOACSA-N Heavy water Chemical compound [2H]O[2H] XLYOFNOQVPJJNP-ZSJDYOACSA-N 0.000 description 2
- 238000006356 dehydrogenation reaction Methods 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 230000008595 infiltration Effects 0.000 description 2
- 238000001764 infiltration Methods 0.000 description 2
- 238000010587 phase diagram Methods 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- WKBPZYKAUNRMKP-UHFFFAOYSA-N 1-[2-(2,4-dichlorophenyl)pentyl]1,2,4-triazole Chemical compound C=1C=C(Cl)C=C(Cl)C=1C(CCC)CN1C=NC=N1 WKBPZYKAUNRMKP-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 238000009659 non-destructive testing Methods 0.000 description 1
- 238000005025 nuclear technology Methods 0.000 description 1
- 238000004321 preservation Methods 0.000 description 1
- 238000005086 pumping Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 239000007790 solid phase Substances 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 239000011031 topaz Substances 0.000 description 1
- 229910052853 topaz Inorganic materials 0.000 description 1
- 238000009827 uniform distribution Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 150000003746 yttrium Chemical class 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
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- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B6/00—Hydrides of metals including fully or partially hydrided metals, alloys or intermetallic compounds ; Compounds containing at least one metal-hydrogen bond, e.g. (GeH3)2S, SiH GeH; Monoborane or diborane; Addition complexes thereof
- C01B6/02—Hydrides of transition elements; Addition complexes thereof
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- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C5/00—Moderator or core structure; Selection of materials for use as moderator
- G21C5/12—Moderator or core structure; Selection of materials for use as moderator characterised by composition, e.g. the moderator containing additional substances which ensure improved heat resistance of the moderator
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Abstract
The invention discloses a crack-free yttrium hydride neutron moderating material for a space reactor, which consists of the following elements in percentage by mass: the total mass percentage of Y and H is more than 99.00 percent, the mass percentage of H is more than 1.83 percent, and the balance is inevitable impurities; the invention also discloses a preparation method of the material, which comprises the following steps: firstly, cold-pressing and molding metal yttrium powder; and secondly, sequentially vacuumizing, introducing hydrogen and sintering. The invention limits the element composition and content, improves the hydrogen atom density in the yttrium hydride, ensures the fast moderating performance of the yttrium hydride, and avoids the influence of metal impurity elements on the thermal stability, the neutron moderating performance and the neutron economy; the invention adopts a powder metallurgy method, utilizes sintering shrinkage to offset the expansion effect of yttrium metal crystal lattices in the hydrogenation process, reduces internal stress, prepares the yttrium hydride neutron moderating material with high density, high hydrogen content and no cracks, and is suitable for manufacturing neutron moderating components with good high-temperature thermal stability of space reactors.
Description
Technical Field
The invention belongs to the technical field of space nuclear reactors and nuclear propulsion, and particularly relates to a crack-free yttrium hydride neutron moderating material for space reactors and a preparation method thereof.
Background
The development of a strategic new industry needs to accelerate the development of the fields of robust aerospace and space exploration. The micro modular or compact advanced reactor is a nuclear technology which is newly developed in the world due to the small size, high power output and low cost of the micro modular or compact advanced reactor, and has potential application value in the aspect of providing a power supply for a space nuclear reactor. Compared with other hydrogen-containing materials such as light water, heavy water and the like, the space stack adopts metal hydride as a neutron moderator material, because the material can keep higher hydrogen atom density at high temperature. Zirconium hydride (ZrH) is adopted in the traditional space reactor design 2-x ) As neutron moderator material, russian TOPAZ and TRIGA space stack in the united states are exemplified. However, zirconium hydride will undergo dehydrogenation at temperatures above 875 ℃, which is highly detrimental to high temperature reactors. In contrast, Yttrium Hydride (YH) 2-x ) Can still maintain higher hydrogen atom density under the high-temperature environment of 1350 ℃ without dehydrogenation phenomenon, thus having potential application value in a high-temperature space reactor.
However, the challenge of producing large-format crack-free yttrium hydride neutron moderating materials with complex geometries arises from the inherent material challenges associated with the hydrogenation process. First, bulk metal yttrium hydrogen absorption reactions are associated with the entry of hydrogen atoms into interstitial sites of the metal lattice, resulting in significant volume expansion and embrittlement of the metal. This variation can produce severe internal stresses in the bulk metal hydride because the diffusion nature of the hydrogenation process can lead to large hydrogen concentration gradients, and the stresses generated at the interface between the hydride shell and interior following growth of the hydride formation can easily exceed the hydride fracture strength and lead to extensive cracking. Second, the direct reaction of yttrium metal with hydrogen to form hydride is usually carried out in a vacuum, isolated vessel, with tight pressure control to ensure product purity. Due to the problems associated with producing large-scale, leak-free hydrogen pressure vessels, it is difficult to manufacture large, crack-free yttrium hydride materials of complex shape using the direct hydrogenation process. Therefore, it is very necessary to search for a new preparation method of metal hydride monoliths to solve the cracking problem of the yttrium hydride neutron moderating material caused by the direct hydrogenation method.
Methods and process routes for preparing high-hydrogen-content and crack-free yttrium hydride neutron moderating materials by powder metallurgy methods are currently rarely reported systematically.
Disclosure of Invention
The invention aims to solve the technical problem of providing a crack-free yttrium hydride neutron moderating material for a space stack aiming at the defects of the prior art. The yttrium hydride neutron moderating material obtains the yttrium hydride neutron moderating material with the H content of more than 1.83% by mass through the limitation on the composition and the content of each element, so that the atomic ratio of yttrium hydride is not less than 1.65, the density of hydrogen atoms in yttrium hydride is greatly improved, the rapid moderating performance of the yttrium hydride neutron moderating material is ensured, the influences of metal impurity elements on the thermal stability, the neutron moderating performance and the neutron economy of the yttrium hydride neutron moderating material are avoided, and the yttrium hydride neutron moderating material is suitable for manufacturing neutron moderating components with good high-temperature thermal stability of a space reactor.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a crack-free yttrium hydride neutron moderating material for a space reactor is characterized by comprising the following elements in percentage by mass: the total mass percentage of Y and H is more than 99.00 percent, the mass percentage of H is more than 1.83 percent, and the balance is inevitable impurities; the inevitable impurities comprise Fe, Si, Ca, W, O and C, wherein Fe is less than or equal to 0.05 percent, Si is less than or equal to 0.05 percent, Ca is less than or equal to 0.05 percent, W is less than or equal to 0.20 percent, O is less than or equal to 0.30 percent, and C is less than or equal to 0.03 percent; the surface and the interior of the crack-free yttrium hydride neutron moderating material do not contain cracks, and the bulk density is not less than 4.0g/cm 3 The atomic ratio of hydrogen to yttrium is not less than 1.65, and the nano-indentation hardness is not less than 2.3 GPa.
According to the invention, the yttrium hydride neutron moderating material with the H mass percentage content of more than 1.83% is obtained by limiting the total mass percentage content of Y and H, the mass percentage content of H, and the composition and content of inevitable impurities in the yttrium hydride neutron moderating material, so that the atomic ratio of yttrium hydride is not less than 1.65, the density of hydrogen atoms in yttrium hydride is greatly improved, and fission neutrons with the average energy of 2MeV released by a fission reactor can be effectively and rapidly moderated. Meanwhile, because the metallic impurity elements often contain larger neutron absorption interfaces, the critical mass of effective neutrons participating in fission reaction in a reactor can be seriously absorbed, so that the neutron economy is seriously reduced, the fission reaction is not facilitated to be carried out, and the metallic impurity elements can reduce the thermal stability of the yttrium hydride neutron moderating material in the high-temperature reactor service process.
In addition, the invention also provides a method for preparing the crack-free yttrium hydride neutron moderating material for the space stack, which is characterized by comprising the following steps:
step one, selecting high-purity metal yttrium powder, and performing cold press molding to a designed shape to obtain a metal yttrium pressed blank;
and step two, putting the yttrium metal pressing blank obtained in the step one into a molybdenum boat, then integrally putting the molybdenum boat into a high-temperature hydrogenation furnace, and sequentially carrying out vacuumizing, hydrogen introducing and sintering processes to obtain the crack-free yttrium hydride neutron moderating material.
Aiming at the defects that the volume expansion of a yttrium hydride block generates large internal stress and further large cracks on the surface and internal microcracks are inevitably introduced in the conventional hydrogen permeation process along with the increase of the hydrogen content, the invention adopts a powder metallurgy method, firstly presses yttrium metal powder into a designed shape to form yttrium metal pressing blank, then sinters the yttrium metal pressing blank in a hydrogen atmosphere, effectively counteracts the expansion effect of yttrium metal crystal lattices in the hydrogenation process by utilizing sintering shrinkage, reduces the internal stress in the yttrium hydride neutron moderating material, and avoids the cracking of the yttrium hydride neutron moderating material caused by the cracks.
Meanwhile, the block density of the yttrium hydride neutron moderating material is improved by the large pressing pressure in the cold press molding, but the hydrogen permeation efficiency is reduced to a certain extent by the compact powder pores, so that the hydrogen content of the sintered block is reduced. According to the invention, by strictly controlling the pressure and the pressure maintaining time of cold press molding and key process parameters such as the temperature rising/reducing rate, the hydrogen introducing rate, the hydrogen gas pressure and the like in the hydrogen infiltration sintering process, the change relation of mutual competition between the hydrogen content and the block density of the yttrium hydride material prepared by powder metallurgy sintering and hydrogen infiltration processes is effectively balanced under the condition of meeting the requirement of yttrium hydride neutron moderation performance, and the purposes of controlling the block density, the hydrogen yttrium atomic ratio and the phase composition of the yttrium hydride neutron moderation material are achieved. Therefore, the yttrium hydride neutron moderating material prepared by the invention has excellent processing performance and mechanical property, is beneficial to preparing large-scale and complex-shaped yttrium hydride neutron moderating materials, and is suitable for being used as a structural material for preparing neutron moderating components for space reactors.
The method is characterized in that in the step one, the grain diameter of the metal yttrium powder is 200-400 meshes, the pressure of cold press molding is 100-250 MPa, and the pressure maintaining time is 3-10 min. Under the action of the pressure and the pressure maintaining time of the cold press molding, the pre-hydrogenated yttrium metal powder forms yttrium metal pressing blanks with high density and uniform distribution in all directions, the blanks have high strength and small internal stress, the metallurgical defects of cracking, layering and the like of yttrium hydride in the subsequent hydrogenation sintering process are effectively overcome, and the large-size and crack-free yttrium hydride neutron moderating material is obtained.
The method is characterized in that in the step two, the vacuum pumping is carried out until the vacuum degree is 10 -2 Pa~10 -1 And after Pa, introducing high-purity hydrogen into the high-temperature hydrogenation furnace at the flow rate of 0.1-0.8L/min, and ensuring that the hydrogen pressure is not less than 0.1MPa until the sintering process is finished. The invention is a Y-H balance systemThe research shows that the hydrogen content in the yttrium hydride neutron moderating material depends on the reaction rate in the hydrogenation process and the diffusion rate of hydrogen in yttrium, namely the hydrogen content in the phase-change hydrogen absorption stage is determined by the sintering temperature and the hydrogen pressure, therefore, the hydrogenation reaction rate is strictly controlled by controlling the introduction flow rate and the hydrogen pressure of hydrogen and adopting a moderating hydrogen introduction mode, so that the yttrium metal pressing blank has sufficient time in the solid solution hydrogen absorption reaction and the phase-change hydrogen absorption reaction process to release internal stress caused by volume expansion of the yttrium hydride material, and cracks on the surface and in the yttrium hydride neutron moderating material are obviously eliminated.
The method is characterized in that the sintering process in the step two comprises the following specific processes: raising the temperature from room temperature to 1000-1300 ℃ at the speed of 5-10 ℃/min, preserving the temperature for 1-6 h, then reducing the temperature to 500-600 ℃ at the speed of 0.1-0.5 ℃/min, then cooling to room temperature along with the furnace, and stopping introducing hydrogen. The temperature rise process in the optimized sintering process effectively ensures the alloying process of the yttrium metal pressing blank, comprehensively optimizes the change relationship among the sintering temperature, the equilibrium vapor pressure and the atomic ratio of yttrium hydride, obviously improves the bulk density and the hydrogen-zirconium ratio of the yttrium hydride neutron moderating material, simultaneously promotes the full implementation of the phase change hydrogen absorption reaction by controlling the sufficient equilibrium heat preservation time in the sintering process, ensures the uniformity of hydrogen element distribution, reduces the pressure caused by hydrogen concentration gradient, and effectively inhibits the generation of cracks in the yttrium hydride neutron moderating material; in addition, the purpose of quasi-static temperature change is achieved by adopting slow-rate temperature reduction, so that the hydrogen absorption rate of the metal yttrium cannot be remarkably changed suddenly, and obvious cracks caused by stress concentration in a short time are avoided.
Compared with the prior art, the invention has the following advantages:
1. according to the invention, the yttrium hydride neutron moderating material with the H content of more than 1.83% by mass is obtained by limiting the composition and content of each element in the yttrium hydride neutron moderating material, so that the atomic ratio of yttrium hydride is not less than 1.65, the hydrogen atom density in yttrium hydride is greatly improved, the rapid moderating performance of yttrium hydride is ensured, the influence of metal impurity elements on the thermal stability, neutron moderating performance and neutron economy of the yttrium hydride neutron moderating material is avoided, and the yttrium hydride neutron moderating material is suitable for manufacturing a neutron moderating component with good high-temperature thermal stability of a space reactor.
2. According to the invention, a powder metallurgy method is adopted, the pressed yttrium metal blank obtained by pressing is sintered in a hydrogen atmosphere, the expansion effect of yttrium metal crystal lattices in the hydrogenation process is effectively counteracted by sintering shrinkage, the internal stress in the yttrium hydride neutron moderating material is reduced, the yttrium hydride neutron moderating material is prevented from cracking due to cracks, the preparation of the large-size and complex-shaped yttrium hydride neutron moderating material is facilitated, and the yttrium hydride neutron moderating material is suitable for being used as a material required by the preparation of neutron moderating components of a space nuclear reactor.
3. Compared with the yttrium hydride material prepared by the conventional block hydrogen permeation method, the yttrium metal pressing blank prepared by cold pressing has larger specification (can reach the ton level), and the prepared yttrium hydride neutron moderating material still has excellent mechanical property and processing property when used for preparing a large-size neutron moderating component, a plurality of pore passages are easy to process on the component, yttrium hydride cracks can not be formed, and the problem of inevitable cracks in the preparation process of the yttrium hydride neutron moderating material is effectively solved.
4. In the hydrogenation process, on one hand, the reaction of gas phase and solid phase in the hydrogenation process tends to be balanced by adopting slow hydrogenation so as to reduce the hydrogen concentration gradient of different areas in the yttrium hydride, and on the other hand, the temperature is slowly reduced in a phase change area so as to ensure that the pressure in the yttrium hydride has enough time to release, and the two aspects of the slow temperature reduction and the slow temperature reduction act synergistically, so that cracks on the surface and in the yttrium hydride material are further avoided.
The technical solution of the present invention is further described in detail by the accompanying drawings and examples.
Drawings
FIG. 1 is a diagram showing the result of RT-ray nondestructive testing of crack-free yttrium hydride neutron moderating material prepared in example 1 of the present invention.
FIG. 2 is an XRD phase diagram of a crack-free yttrium hydride neutron moderating material prepared in example 1 of the present invention.
Detailed Description
Example 1
The crack-free yttrium hydride neutron moderating material of the embodiment comprises the following elements in percentage by mass: the total mass percentage of Y and H is 99.00%, the mass percentage of H is 1.83%, and the balance is inevitable impurities.
The preparation method of the crack-free yttrium hydride neutron moderating material comprises the following steps:
step one, selecting metal yttrium powder with the mass purity of 99.5 percent, and performing cold press molding to the metal yttrium powder to a designed shape to obtain a metal yttrium pressed blank; the grain diameter of the metal yttrium powder is 200 meshes, the pressure of cold press molding is 100MPa, and the pressure maintaining time is 3 min;
step two, putting the yttrium metal pressing blank obtained in the step one into a molybdenum boat, then putting the whole body into a high-temperature hydrogenation furnace, and vacuumizing until the vacuum degree is 10 -2 After Pa, introducing hydrogen with the mass purity of 99.95% into a high-temperature hydrogenation furnace at the flow rate of 0.1L/min, and sintering, and ensuring the hydrogen pressure to be 0.1MPa until the sintering process is finished to obtain the crack-free yttrium hydride neutron moderating material; the sintering process comprises the following specific steps: firstly heating from room temperature to 1000 ℃ at the speed of 5 ℃/min, preserving heat for 1h, then cooling to 500 ℃ at the speed of 0.1 ℃/min, then cooling to room temperature along with the furnace, and stopping introducing hydrogen.
Through detection, the inevitable impurities in the crack-free yttrium hydride neutron moderating material prepared in the embodiment include Fe, Si, Ca, W, O and C, and the mass percentages of the impurities are as follows: fe =0.05%, Si =0.05%, Ca =0.05%, W =0.20%, O =0.30%, C = 0.03%; the surface and the interior of the crack-free yttrium hydride neutron moderating material do not contain cracks, and the bulk density is 4.0g/cm 3 The atomic ratio of yttrium hydride is 1.65, and the nano indentation hardness is 2.3 GPa.
Fig. 1 is a diagram of the RT ray nondestructive test result of the crack-free yttrium hydride neutron moderating material prepared in this embodiment, and as can be seen from fig. 1, the yttrium hydride neutron moderating material does not contain microcracks on the surface and does not have any obvious cracks inside, which illustrates that the powder metallurgy sintering and hydrogenation process route adopted in the present invention effectively avoids the generation of cracks in the yttrium hydride neutron moderating material.
Fig. 2 is an XRD phase diagram of the crack-free yttrium hydride neutron moderating material prepared in this example, and as can be seen from fig. 2, all the phases of the yttrium hydride neutron moderating material are yttrium hydride structures, and no phase of metal yttrium appears, which illustrates that the preparation process of the present invention does not cause the problem of high temperature hydrogen loss of yttrium hydride.
Example 2
The crack-free yttrium hydride neutron moderating material of the embodiment comprises the following elements in percentage by mass: the total mass percentage of Y and H is 99.2%, the mass percentage of H is 2.02%, and the balance is inevitable impurities.
The preparation method of the crack-free yttrium hydride neutron moderating material comprises the following steps:
step one, selecting metal yttrium powder with the mass purity of 99.5 percent, and performing cold press molding to the metal yttrium powder to a designed shape to obtain a metal yttrium pressed blank; the grain diameter of the metal yttrium powder is 325 meshes, the pressure of the cold press molding is 220MPa, and the pressure maintaining time is 6 min;
step two, putting the yttrium metal pressing blank obtained in the step one into a molybdenum boat, then putting the whole body into a high-temperature hydrogenation furnace, and vacuumizing until the vacuum degree is 10 -1 After Pa, introducing hydrogen with the mass purity of 99.95% into a high-temperature hydrogenation furnace at the flow rate of 0.5L/min, and sintering, and ensuring the hydrogen pressure to be 0.3MPa until the sintering process is finished to obtain the crack-free yttrium hydride neutron moderating material; the sintering process comprises the following specific steps: heating from room temperature to 1200 ℃ at the speed of 10 ℃/min, preserving heat for 3h, then cooling to 550 ℃ at the speed of 0.3 ℃/min, cooling to room temperature along with the furnace, and stopping introducing hydrogen.
Through detection, the inevitable impurities in the crack-free yttrium hydride neutron moderating material prepared in the embodiment include Fe, Si, Ca, W, O and C, and the mass percentages of the impurities are as follows: fe =0.042%, Si =0.045%, Ca =0.038%, W =0.15%, O =0.20%, C = 0.02%; the surface and the interior of the crack-free yttrium hydride neutron moderating material do not contain cracks, and the bulk density is 4.12/cm 3 The atomic ratio of yttrium hydride is 1.82, and the nano indentation hardness is 2.3 GPa.
Example 3
The crack-free yttrium hydride neutron moderating material of the embodiment comprises the following elements in percentage by mass: the total mass percentage of Y and H is 99.20%, the mass percentage of H is 2.03%, and the balance is inevitable impurities.
The preparation method of the crack-free yttrium hydride neutron moderating material comprises the following steps:
step one, selecting metal yttrium powder with the mass purity of 99.5 percent, and performing cold press molding to the metal yttrium powder to a designed shape to obtain a metal yttrium pressed blank; the grain diameter of the metal yttrium powder is 400 meshes, the pressure of cold press molding is 250MPa, and the pressure maintaining time is 10 min;
step two, putting the yttrium metal pressing blank obtained in the step one into a molybdenum boat, then putting the whole body into a high-temperature hydrogenation furnace, and vacuumizing until the vacuum degree is 10 -2 After Pa, introducing hydrogen with the mass purity of 99.99 percent into a high-temperature hydrogenation furnace at the flow rate of 0.8L/min for sintering, and ensuring the hydrogen pressure to be 0.5MPa until the sintering process is finished to obtain a crack-free yttrium hydride neutron moderating material; the sintering process comprises the following specific steps: heating from room temperature to 1300 ℃ at the speed of 6 ℃/min, preserving heat for 6h, then cooling to 600 ℃ at the speed of 0.5 ℃/min, cooling to room temperature along with the furnace, and stopping introducing hydrogen.
Through detection, the inevitable impurities in the crack-free yttrium hydride neutron moderating material prepared in the embodiment include Fe, Si, Ca, W, O and C, and the mass percentages of the impurities are as follows: fe =0.03%, Si =0.02%, Ca =0.02%, W =0.10%, O =0.20%, C = 0.01%; the surface and the interior of the crack-free yttrium hydride neutron moderating material do not contain cracks, and the bulk density is 4.20g/cm 3 The atomic ratio of yttrium hydride is 2.0, and the nano indentation hardness is 2.9 GPa.
The above description is only for the preferred embodiment of the present invention, and is not intended to limit the present invention in any way. Any simple modification, change and equivalent changes of the above embodiments according to the technical essence of the invention are still within the protection scope of the technical solution of the invention.
Claims (5)
1. A crack-free yttrium hydride neutron moderating material for space reactorIs characterized by comprising the following elements in percentage by mass: the total mass percentage of Y and H is more than 99.00 percent, the mass percentage of H is more than 1.83 percent, and the balance is inevitable impurities; the inevitable impurities comprise Fe, Si, Ca, W, O and C, wherein Fe is less than or equal to 0.05 percent, Si is less than or equal to 0.05 percent, Ca is less than or equal to 0.05 percent, W is less than or equal to 0.20 percent, O is less than or equal to 0.30 percent, and C is less than or equal to 0.03 percent; the surface and the interior of the crack-free yttrium hydride neutron moderating material do not contain cracks, and the bulk density is not less than 4.0g/cm 3 The atomic ratio of hydrogen to yttrium is not less than 1.65, and the nano-indentation hardness is not less than 2.3 GPa.
2. A method of preparing a crack-free yttrium hydride neutron moderating material for a space stack according to claim 1, comprising the steps of:
step one, selecting high-purity metal yttrium powder, and performing cold press molding to a designed shape to obtain a metal yttrium pressed blank;
and step two, putting the yttrium metal pressing blank obtained in the step one into a molybdenum boat, then integrally putting the molybdenum boat into a high-temperature hydrogenation furnace, and sequentially carrying out vacuumizing, hydrogen introducing and sintering processes to obtain the crack-free yttrium hydride neutron moderating material.
3. The method according to claim 2, wherein the particle size of the metal yttrium powder in the first step is 200-400 meshes, the pressure of the cold press molding is 100-250 MPa, and the pressure holding time is 3-10 min.
4. The method of claim 2, wherein the vacuum is applied to a vacuum level of 10 in step two -2 Pa~10 -1 And after Pa, introducing high-purity hydrogen into the high-temperature hydrogenation furnace at the flow rate of 0.1-0.8L/min, and ensuring that the hydrogen pressure is not less than 0.1MPa until the sintering process is finished.
5. The method according to claim 2, wherein the sintering process in the second step comprises the following specific processes: raising the temperature from room temperature to 1000-1300 ℃ at the speed of 5-10 ℃/min, preserving the temperature for 1-6 h, then reducing the temperature to 500-600 ℃ at the speed of 0.1-0.5 ℃/min, then cooling to room temperature along with the furnace, and stopping introducing hydrogen.
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